Mechanical and chemical-mechanical planarizing processes (collectively "CMP") are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrates and substrate assemblies. FIG. 1 schematically illustrates a conventional CMP machine 10 having a platen 20. The platen 20 supports a planarizing medium 40 that can include a polishing pad 41 having a planarizing surface 42 on which a planarizing liquid 43 is disposed. The polishing pad 41 may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a fixed-abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid 43 may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the wafer, or the planarizing liquid may be a planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed abrasive polishing pads.
The CMP machine 10 can also include an underpad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the polishing pad 41. A drive assembly 26 rotates the platen 20 (as indicated by arrow A), and/or it reciprocates the platen 20 back and forth (as indicated by arrow B). Because the polishing pad 41 is attached to the underpad 25, the polishing pad 41 moves with the platen 20.
A wafer carrier 30 is positioned adjacent the polishing pad 41 and has a lower surface 32 to which a substrate 12 may be attached via suction. Alternatively, the substrate 12 may be attached to a resilient pad 34 positioned between the substrate 12 and the lower surface 32. The wafer carrier 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 33 may be attached to the wafer carrier to impart axial and/or rotational motion (as indicated by arrows C and D, respectively).
To planarize the substrate 12 with the CMP machine 10, the wafer carrier 30 presses the substrate 12 face-downward against the polishing pad 41. While the face of the substrate 12 presses against the polishing pad 41, at least one of the platen 20 or the wafer carrier 30 moves relative to the other to move the substrate 12 across the planarizing surface 42. As the face of the substrate 12 moves across the planarizing surface 42, material is continuously removed from the face of the substrate 12.
FIG. 2 is a partially schematic isometric view of a conventional web-format planarizing machine 10a that has a table 11 with a support surface 13. The support surface 13 is a generally rigid panel or plate attached to the table 11 to provide a flat, solid workstation for supporting a portion of a web-format planarizing pad 40a in a planarizing zone "E" during planarization. The planarizing machine 10a also has a pad advancing mechanism, including a plurality of rollers, to guide, position, and hold the web-format pad 40a over the support surface 13. The pad advancing mechanism generally includes a supply roller 24, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. As explained below, a motor (not shown) drives the take-up roller 23 to advance the pad 40a across the support surface 13 along a travel path T--T. The motor can also drive the supply roller 24. The first idler roller 21 a and the first guide roller 22a press an operative portion of the pad 40a against the support surface 13 to hold the pad 40a stationery during operation.
The planarizing machine 10a also has a carrier assembly 30a to translate the substrate 12 over the pad 40a. In one embodiment, the carrier assembly 30a has a head 31 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. The carrier assembly 30a also has a support gantry 34 and a drive assembly 35 that can move along the gantry 34. The drive assembly 35 has an actuator 36, a drive shaft 37 coupled to the actuator 36 and an arm 38 projecting from the drive shaft 37. The arm 38 carries the head 31 via a terminal shaft 39. The actuator 36 orbits the head 31 about an axis F--F (as indicated by arrow R.sub.1) and can rotate the head 31 (as indicated by arrow R.sub.2) to move the substrate 12 over the polishing pad 40a while a planarizing fluid 43a flows from a plurality of nozzles 45 in the head 31. The planarizing fluid 43a may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the substrate 12, or the planarizing fluid 43a may be a non-abrasive planarizing solution without abrasive particles, as was discussed above with reference to FIG. 1.
In the operation of the planarizing machine 10a, the polishing pad 40a moves across the support surface 13 along the travel path T--T either during or between planarizing cycles to change the particular portion of the polishing pad 40a in the planarizing zone E. For example, the supply and take-up rollers 24 and 23 can drive the polishing pad 40a between planarizing cycles such that a point P moves incrementally across the support surface 13 to a number of intermediate locations I.sub.1, I.sub.2, etc. Alternatively, the rollers 24 and 23 may drive the polishing pad 40a between planarizing cycles such that the point P moves all the way across the support surface 13 to completely remove a used portion of the polishing pad 40a from the planarizing zone E. The rollers 23 and 24 may also continuously drive the polishing pad 40a at a slow rate during a planarizing cycle such that the point P moves continuously across the support surface 13 during planarization. In any case, the motion of the polishing pad 40a is generally relatively slow when the substrate 12 engages the polishing pad 40a, and the relative motion between the substrate 12 and the polishing pad 40a is primarily due to the motion of the head 31. Generally, the polishing pad 40a is oriented horizontally to ensure that it is perpendicular to the orbit axis F--F of the head 31, and to keep the planarizing fluid 43a on the polishing pad 40a.
CMP processes should consistently and accurately produce a uniform, planar surface on substrates to enable circuit and device patterns to be formed with photolithography techniques. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the photo-patterns to within a tolerance of approximately 0.1 microns. Focussing photo-patterns to such small tolerances, however, is difficult when the planarized surfaces of the substrates are not uniformly planar. Thus, to be effective, CMP processes should create highly uniform, planar surfaces on the substrates.
One drawback with the arrangement shown in FIG. 2 is that it can be inefficient to periodically remove and replace the polishing pad 40a. For example, it can be awkward and time consuming to thread the polishing pad 40a from a new supply roller 24, through the idler rollers 21a and 21b, through the guide rollers 22a and 22b and then attach the polishing pad 40a to the take-up roller 23.
Another drawback with the arrangements shown in both FIGS. 1 and 2 is that the material removed from the substrate and/or the polishing pad can remain on the polishing pad as the planarizing operation continues. The removed material can damage the substrate, for example, by becoming caught between the polishing pad and the substrate and scratching or otherwise adversely affecting the surface of the substrate.
Still another drawback with some conventional arrangements is that ventilation air is generally directed downwardly toward the polishing pad striking the polishing pad at an approximately 90.degree. angle. As the air strikes the polishing pad, it typically becomes turbulent, which can separate dried particles or agglomerations of dried particles from the planarizing machine and allow such particles to settle on the polishing pad where they can scratch the substrate 12. The turbulent ventilation air can also be difficult to collect and exhaust from the region adjacent the polishing pad 40a.
One conventional approach to addressing some of the foregoing drawbacks is to position the substrate against a continuous vertical polishing pad and move the polishing pad at a high speed relative to the substrate, in the manner of a belt sander. FIG. 3 is a partially schematic, side elevation view of one such conventional CMP apparatus 10b having two rollers 25 and a continuous polishing pad 40b extending around the two rollers 25. The polishing pad 40b can be supported by a continuous support band 41, formed from a flexible material, such as a thin sheet of stainless steel. A pair of platens 20b provide additional support for the polishing pad 40b at two opposing planarizing stations. Two carriers 30b aligned with the platens 20b at the planarizing stations can each bias a substrate 12 against opposing outwardly facing portions of the polishing pad 40b. Devices such as the apparatus 10b shown in FIG. 3 are available from Aplex, Inc. of Sunnyvale, Calif. under the name AVERA.TM.. Similar devices with a horizontally oriented polishing pad 40b and a single carrier 30b are available from Lam Research Corp. of Fremont, Calif.
During operation, the continuous polishing pad 40b moves at a relatively high speed around the rollers 25 while the carriers 30b press the substrates 12 against the polishing pad 40b. An abrasive slurry or other planarizing liquid having a suspension of abrasive particles is introduced to the surface of the polishing pad 40b which, in combination with the motion of the polishing pad 40b relative to the substrates 12, mechanically removes material from the substrates 12.
One drawback with the continuous polishing pad device shown in FIG. 3 is that the polishing pad 40b must move at a high speed to effectively planarize the substrates 12, which can present a safety hazard to personnel positioned nearby, for example, if the polishing pad 40b should break, loosen or otherwise malfunction during operation. Another drawback is that once a defect forms in the polishing pad 40b, it can affect each subsequent substrate 12. The combined polishing pad 40b/support band 41 may also wear more quickly than other polishing pads because both a planarizing surface 42b of the polishing pad 40b and a rear surface 44 of the support band 41 rub against relatively hard materials (e.g., the polishing pad 40b rubs against the substrate 12 and the support band 41 rubs against the platen 20b). Still another drawback is that the interface between the support band 41 and the platen 20b can be difficult to seal, due to the high speed of the support band 41, and can therefore be susceptible to abrasion by the abrasive slurry. Furthermore, the abrasive slurry itself is generally expensive because it contains a suspension of abrasive particles and therefore the apparatus 10b can be expensive to operate because the abrasive slurry runs off the polishing pad 40b and must be replenished.